In addition to Tabaluga's comments, I would like to add that, selecting the cells that are living via these methods is a sort of selection pressure on the surviving cells, which means that the Jurkat cells you now have are no longer Jurkats - so unless these cells are particularly precious (e.g. stable cell line, in which case they aren't Jurkats any more either) then it is best to throw them out and get a fresh batch up.